In rubbers for tire treads and the like, low-vinyl polybutadiene rubbers, low-styrene or low-vinyl styrene-butadiene copolymer rubbers have conventionally been used by way of example to improve abrasion resistance.
Rubber compositions containing such a low-vinyl or low-styrene rubber as a principal component are however accompanied by the drawback that they are lowered in wet skid resistance, an important characteristic required for tire treads.
Use of a rubber composition containing a high-vinyl polybutadiene or a high-styrene styrene-butadiene copolymer rubber for improved wet skid resistance however results in a reduction in abrasion resistance. Especially, high-styrene styrene-butadiene copolymer rubbers are accompanied by the drawback that rebound is reduced to lead to increased tire rolling resistance.
In the meantime, the present inventors have already found that the rebound of a diene polymer can be significantly improved by the introduction of specific atomic groups in the polymer through a reaction of the diene polymer having active alkali metal and/or alkaline earth metal terminals, with a compound containing in the molecule thereof a ##STR2## in which M stands for an oxygen or sulfur atom (U.S. Pat. No. 4,647,625). In addition, it has already been found that the diene rubber polymer with the atomic groups introduced therein has been improved not only in rebound but also in abrasion resistance and wet skid resistance. However, the abrasion resistance so improved cannot be considered high enough to sufficiently meet the level required in recent years, resulting in a demand for a still greater improvement.
On the other hand, rubber compositions blended with a styrene-butadiene copolymer rubber containing butadiene units of a high trans content are dealt with, for example, in Japanese Patent Application Laid-Open No. 100146/1982. Primary objects however reside in improvements in processing characteristics and cold flow characteristics and also in improvements in the wet skid resistance reduced due to the use of the copolymer rubber. As a matter of fact, abrasion resistance is improved very little.